Countermeasures to Reduce Sensorimotor Impairment and Space Motion Sickness Resulting From Altered Gravity Levels

Primary outcomes

1. Percent Change in Roll Tilt Perception After Exposure to Hypogravity

   Time frame: 1 session

   Note that this applies to arms 1-4 only.

   Subjects sat on a chair on a moving platform on top of a centrifuge that created an artificial gravity environment. Subjects were repeatedly roll tilted to angles between 11 and 19 degrees, and then reported their perceived tilt angle using a subjective visual vertical task. They did this while experiencing centripetal acceleration equivalent to Earth gravity (1 Gz), and then hypogravity (0.5 Gz). We hypothesized that, after entering hypogravity, subjects would tend to underestimate their tilt angle. We calculated the percent change in their perception of tilt between 1 Gz and 0.5 Gz.

2. Yaw Perceptual Motion Threshold

   Time frame: 2 sessions separated by at least four days; measurements made 2 hrs after ingestion of medication

   This is a perceptual self-motion threshold that measures the precision of the vestibular system. It is analogous to an audiogram, but for motion. Subjects sat on a motorized platform which repeatedly provided them with small motions to the left or right. After each motion subjects report whether they perceived a motion to the left or right. Based on subject responses, a psychometric curve fit is performed that determines the threshold (the standard deviation of the underlying cumulative Gaussian). Yaw rotation means rotations about an axis that is perpendicular to gravity.

   This outcome measure applies only to arm 5 subjects.

3. Roll Perceptual Motion Threshold

   Time frame: 2 sessions separated by at least four days; measurements made 2 hrs after ingestion of medication

   This is a perceptual self-motion threshold that measures the precision of the vestibular system. It is analogous to an audiogram, but for motion. Subjects sat on a motorized platform which repeatedly provided them with small motions to the left or right. After each motion subjects report whether they perceived a motion to the left or right. Based on subject responses, a psychometric curve fit is performed that determines the threshold (the standard deviation of the underlying cumulative Gaussian). Roll tilt means rotations about an axis that is Earth-horizontal.

   This outcome measure applies only to arm 5 subjects.

4. Interaural Perceptual Motion Threshold

   Time frame: 2 sessions separated by at least four days; measurements made 2 hrs after ingestion of medication

   This is a perceptual self-motion threshold that measures the precision of the vestibular system. It is analogous to an audiogram, but for motion. Subjects sat on a motorized platform which repeatedly provided them with small motions to the left or right. After each motion subjects report whether they perceived a motion to the left or right. Based on subject responses, a psychometric curve fit is performed that determines the threshold (the standard deviation of the underlying cumulative Gaussian). Interaural translation refers to translations in the horizontal plane to the subject's left or right.

   This outcome measure applies only to arm 5 subjects.

5. Percent Change in Manual Control Performance After Exposure to Hypogravity

   Time frame: 1 session

   Note that this applies to arms 6-9 only.

   Subjects sat on a chair on a moving platform on top of a centrifuge that created an artificial gravity environment. Subjects completed a manual control task in which their charge was randomly perturbed in roll tilt, and they used a joystick to attempt to keep themselves aligned with upright, while in the dark. They did this while experiencing centripetal acceleration equivalent to Earth gravity (1 Gz), and then hypogravity (0.5 Gz). We calculated their performance by calculating the standard deviation of chair position across time, with a smaller number indicating better performance. Then we calculated the percent change in their performance between 1 Gz and 0.5 Gz.